The objective of the work proposed is development and application of spin-label crosslinking reagents which will provide information about the relative geometry and motions of the protein and glycoprotein components of animal cell membranes. Changes in the geometry and motions of membrane proteins are thought to be associated with many normal and abnormal cell functions. The methods of carrying out this work are to: (1) synthesize lipophilic, bifunctional spin labels from a few synthetic precursors, (2) determine the factors which determine the orientation of these reagents in membranes, (3) apply the reagents to a simplified membrane containing two major proteins derived from red blood cells, (4) apply the reagents to analyze the geometric arrangement of proteins in red blood cells, (5) investigate applications of the new reagents to the malignant transformation of cells.